I've erroneously bought a rim (hoping my technical English is right: the part of the wheel between the spokes and the tire). While I have no immediate use for it, shipping it back to the seller for refund would be a waste of shipping costs if I would need a new rim in the foreseeable future. I have been riding a Gazelle street bike for ~10 years now, and it is showing signs of wear along the periphery. In particular, I've recently discovered I've been negligient with checking the spokes of my rear wheel, which has been running some time with broken spokes. For the second time now in these 10 years.

How long can I reasonably expect rims to last on a street bike? Will I be facing replacements sometime soon?

3 Answers
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The failure mode (other than from accidents) is simply the wearing-down of the brake surfaces over time (see this question). You can literally wear-away the rim surface with your brakes until the rim is too weak.

Some rims designed for commuters have a groove in them that is designed to indicate wear. When you can no longer see the groove, you know its time to replace the rim (might as well replace the wheel).

In addition to brake wear there is the "slings and arrows of outrageous fortune" -- rocks, curbs, manhole covers, etc. Generally hitting an obstacle head-on doesn't damage the rim (much) but, eg, just catching the edge of a raised manhole cover can ding the rim edge pretty well. Plus, over time rough use can cause the spoke nipples to pull through the rim, and riding with broken spokes can distort the rim to where it becomes hard to true.

But if you're not rough on the rim and keep it properly trued it can last a long time. I've generally gotten maybe 15,000 miles out of rims, and if they were replaced it was because I was relacing the wheels anyway and figured new rims wouldn't hurt.

If you mistreat a rim, you can destroy it pretty quickly. For winter riding in Toronto, I used to just accept I was going to destroy a mountain bike every 2-3 years.

One horrible MTB end of life event was climbing a hill in the snow and the steer tube just twisted into a figure 8 and I went over the bars. (Oddly enough my coworkers were driving by and dragged me into the office).

But the worst was a rim failure in traffic. My brake pads, with all the winter grit accumulated had worn through the sides of the rim, and one last brake attempt and the pad locked into the rim, tearing off a strip of metal, and sending me over the handlebars.

I had enough sense as soon as I hit the ground to roll into the snow bank to avoid the cars. Also, I was close enough to the office to carry the bike back, get some work dry clothes on and take a bus home. But a rim can fail badly, if you treat it poorly. It was entirely my own fault. But winter riding can be hard on a bike, and hard to do proper maintenance.